Department of Chemistry, University of Waterloo, 200 University Ave W., Waterloo, ON, N2L3G1, Canada graham.murphy@uwaterloo.ca
› InstitutsangabenThis work was supported by the University of Waterloo and the Natural Sciences and Engineering Research Council (NSERC) of Canada (Discovery Grant 418602-2013).
Dedicated to Professor Victor Snieckus on the occasion of his 80th birthday
Abstract
The use of hypervalent iodine reagents as a general tool for the activation of PPh3 and its application to the functionalization of alcohols is reported. Combination of PPh3 with PhICl2 or TolIF2 gives dihalophosphoranes that are characterized by 31P NMR, however, with PhIOAc2, PhI(OTFA)2, or the cyclic chloro(benzoyloxy)iodane, no phosphoranes were observed. Reaction of these iodanes with PPh3 in the presence of primary, secondary, or tertiary alcohols results in either halogenation or acyl-transfer products in moderate to high yield.
6a For syntheses of Ph3PCl2 with various reagents such as Cl2, CCl4, (COCl)2, COCl2, or C2Cl6, see:
Michaelis A.
Michaelis A.
v. Soden H.
Justus Liebigs Ann. Chem. 1885; 229: 295
20 Reacting Ph3PF2 (4, 1.6 equiv) with 4-nitrophenethyl alcohol for 45 min at 160 °C using 10 mol% TiF3 as an activating agent produced alkyl fluoride 5a in 66% yield.
21 The major competing reaction pathway in these experiments was alcohol dimerization, giving the ether. It is proposed that this arises from the alcohol outcompeting fluoride as the nucleophile. See ref. 16.
22 Zhang and co-workers reported phenethyl acetate to be the major byproduct of a reaction between 5, phenethyl alcohol, hexanoic acid, DMAP, and PPh3. No indication of phenethyl trifluoroacetate was reported for the analogous reaction using iodane 7. See Table S1 in the supporting information of ref. 1a.
23 Only trace amounts of 15a or 15b were visible by 1H NMR analysis of the crude reaction mixtures after 10 min. Prolonging the reaction times to 2–3 h did not significantly change the product ratios, suggesting that the reaction pathways are competing, as opposed to 14 reacting with the benzoate byproduct of the reaction to give 15. Concentrating the reaction mixtures before column chromatography appears to have increased the ratio of the benzoate products.
24
Zhdankin VV.
Koposov AY.
Litvinov DN.
Ferguson MJ.
McDonald R.
Luu T.
Tykwinski RR.
J. Org. Chem. 2005; 70: 6484